The ride height of a vehicle generally is considered to be the elevation of the vehicle body with respect to the vehicle suspension system. Vehicle wheel alignment is closely related to ride height, since over time, changes in the suspension system due to worn or damaged springs, shock absorbers, ball joints or the like can affect wheel alignment. In general, manufacturers' specifications for wheel alignment factors, such as camber and toe, are provided with respect to the suspension system in new condition, that is to say, prior to deterioration of the system as a result of wear. It is therefore important that changes in the suspension system be accounted for prior to performing wheel alignment. Such changes in the suspension system can be determined by comparing the value of the current ride height with the ideal ride height of the suspension system prior to wear. In general, manufacturers as well as providing the wheel alignment factors for an ideal suspension system also provide corresponding factors for suspension systems with varying degrees of wear, which can be determined by variance in the ride height of the vehicle from the original specification.
Devices for determining ride height of a vehicle are known. One type is essentially an electronic measuring tape, which is suitable only for measuring the vertical height of one or more predetermined points on a vehicle body or the suspension system above the ground. In general, this device is unsatisfactory, since, manufacturers often provide ride height data for vehicles as the vertical distance between two predetermined points. One such point may be on the vehicle body, or the suspension system of the vehicle, but fixed relative to the vehicle body. The other manufacturer specified measurement point is normally on the vehicle suspension system, but fixed relative to the ground plane. Such predetermined points, in general are not located vertically one above the other; and in many vehicles the configuration of the suspension system prevents direct measurements. Accordingly, since the apparatus of Strege is only capable of making direct linear measurements, it is entirely unsuitable for measuring the ride height of the majority of vehicles. A further disadvantage of the apparatus of Strege is that the accuracy of the measurement is partially dependent on the operator manually placing the apparatus in the vertical direction, which due to human error may not always occur. Where the ride height of a vehicle is given as a non-vertical dimension, for example, an angular dimension, whereby a line joining the points from which the ride height is to be measured would make an angle with the vertical, in general, the apparatus of Strege is entirely unsuitable.
Another type of prior art measuring device is capable of determining vertical height between respective predetermined points on the vehicle body and suspension system. However, this type of device suffers from one particularly important disadvantage in that the apparatus must be oriented to be in the same vertical plane as the two predetermined points, the vertical distance between which is to be determined. A further disadvantage of the device is that the device must be located on the ground at the same level as the wheels of the vehicle. This is not always possible, particularly if the vehicle is placed over a service pit, or on a ramp. Another disadvantage of this type of device is that it is unsuitable for taking measurements between the outer body of a vehicle and ground level, and in certain cases the manufacturer's specification requires that the ride height of a vehicle is determined by the distance of a point on the vehicle body above ground level.
There is therefore a need for a method and apparatus for determining the ride height dimension of a vehicle which overcomes the problems of known methods and apparatus.